As appears for example from British patent specification No. 556,531, in the known devices for the type stated the transformer unit, comprising a.o. a reactor and a glow switching tube, is mounted within an elongated box arranged above the shade or shades, and the tubular fluorescent lamp, in the following called tube lamp, can from above be inserted in the shade or shades and at the ends of this or these be brought to engage the transformer unit sockets, at said ends extending downwards from the transformer box and being electrically connected to the transformer unit. By such fixtures for tube lamps, however, the renewal of the tube lamp is ackward and owing thereto, that the shade often is not easy of access, difficult to carry through.
By other such combined devices, especially such provided at the underside with a grate to prevent dazzling, it is necessary to take the shade more or less apart before renewal of the tube lamp can take place, wherefore, in such cases the renewal of the tube lamp is complicated and often connected to great danger, especially while often it is necessary for the renewal to use a more or less wobbly ladder standing on which the person taking care of the renewal has to manipulate with various shade parts as well as with a new and an old tube lamp.
Fixtures for tube lamps are also known, however, which are independent of the shades, which are adapted to be directly hanged up on the tube lamp when this is mounted between sockets arranged on the underside of a transformer box, conf. for example British patent specification No. 819,549 and U.S. Pat. No. 4,122,511. From the last said specification it is further known that in certain cases tube lamp before being mounted in the sockets of the fixture is led through openings in the end parts of the shade so that the ends of the tube lamp protrude from one each of the shade end parts. Hereby is obtained the advantage, that the shade may be provided with side and top plates having reflecting inner faces surrounding the discharge tube whereby the greatest possible luminous yield from the discharge tube can be obtained.
Shades of the type stated in the generic part of the main claim and per se known from the said U.S. Pat. No. 4,122,511 makes it possible, provided the discharge tube is located in a prescribed distance from the surface illuminated, to obtain an approximately uniform illumination of this surface over its whole illuminated area, and that is of great importance for example in stores and many offices.
Such shades must be given, however, if they have to be effective, a large height compared with the diameter of the tube lamp, i.e. a height of 3 to 4 times this diameter, and since the transformer box has a height at least not minor than the diameter of the discharge tube, the whole combined fixture and shade has a very large total height. By many arrangements of the fixture, especially if it is desired that the plane of symmetri of the shade has to form an angle with vertical, for example to ensure illumination of articles placed in case racks this great height constitutes an essential disadvantage. Further, the transformer box has to be manufactured separately resulting in the production grewing relatively expensive, especially when the combined fixture and shade has to occur in different shapes adapted to different diameters and lengths of the tube lamp.
This disadvantage appears still more distinct in connection with fixtures not combined with a shade but demanding a shade to be mounted on the tube lamp itself since in such cases shade plus fixture takes up still more space. Further in connection with shades suspended in the tube lamp itself quite a number of manipulations with the different parts are necessary when the tube lamp has to be renewed.